We propose to continue to develop optical methods for monitoring membrane potential. In particular we plan to work in two directions. The first is to develop more sensitive dyes to make the method easier to use. The second is to develop the apparatus for monitoring activity in CNS neurons. At present we can monitor activity (action potentials) in 14 neurons simultaneously. This would be used in an invertebrate ganglion with relatively few cells (100-1000) in an effort to study the neuronal basis of behavior in more detail.